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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Mayfly Species Leptophlebia intermedia (Black Quills)

Where & when

In 8 records from GBIF, adults of this species have been collected during April (75%) and May (25%).

In 4 records from GBIF, this species has been collected at elevations of 20, 643, 719, and 1293 ft.

Species Range

Physical description

Most physical descriptions on Troutnut are direct or slightly edited quotes from the original scientific sources describing or updating the species, although there may be errors in copying them to this website. Such descriptions aren't always definitive, because species often turn out to be more variable than the original describers observed. In some cases, only a single specimen was described! However, they are useful starting points.

Male Spinner

Described in Needham et al (1935) as Blasturus intermedius
Body length: 11-13 mm
Wing length: 8-13 mm

A rather small species, distinguished from all others except B. grandis (now a synonym of L. intermedia) by the distinctive “scarf” type of penes.

Frontal margin of head red-brown; vertex and notum of thorax blackish. Sternum deep reddish black. Pleura dark red-brown with black markings. Fore leg red-brown (orange, in recently transformed specimens), tarsus slightly paler than femur and tibia. Venation orange to reddish brown; no stain at wing roots or in stigmatic area. Abdominal tergites dark red-brown, sternites more yellowish. Ganglionic areas orange; sternite 9 reddish brown. Usual pale oblique submedian streaks on tergites, dark markings at spiracles, and faint dark oblique submedian streaks on sternites. Middle tail fully 2/3 the length of the laterals. Tails dark red-brown, joinings obscurely darker. Penes much as in B. grandis, with the appendages extending backwards almost to end of notch (see fig. 138).

Described as B. grandis

Body length 11-13 mm, wing length 10-13 mm

This is a rather large species of lighter brown color, alternately yellowish brown. Thorax above shining brown with yellow streaks in the notal furrow each side. Legs dull yellow with the tarsi a little paler and the usual lines on the knee caps very narrow. Wings yellowish in front and toward the outer margin; hyaline at the center and toward the rear; hind wings white.

Abdomen pale yellowish brown, paler beneath especially in the middle of the segments. Segments 1 to 6 have the mid-dorsal pale line almost entire, and the paired oblique marks confluent with the pale rings at the base of the segments. The latter give the abdomen a distinctly ringed appearance. The dorsum of 7 to 10 brown, practically without color pattern. Tails white, distinctly ringed with reddish brown. Genitalia as in fig. 138.

This species is larger and paler than others of the genus; the ‘“scarf” type of penes is found only in this species and in B. intermedius (now a synonym of L. intermedia).

Start a Discussion of Leptophlebia intermedia


  • Needham, James G., Jay R. Traver, and Yin-Chi Hsu. 1935. The Biology of Mayflies. Comstock Publishing Company, Inc.

Mayfly Species Leptophlebia intermedia (Black Quills)

Species Range
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